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Forum Discussion
I wanted to reserve a 'static' IP for my security camera
I'm having similar issue. I wanted to reserve a 'static' IP for my security camera. After I pick the MAC address for my camera by clicking the radio button on the left and the very last is to clic...
So basically there are two pools on the Netgear R8000: static (aka AR) and dynamic. If a client device does not request IP, then Netgear looks in the 'static' pool and if the client's MAC address found, then hand out that IP. Else hand out an IP from the dynamic pool.
You said "Rebooting the router clears the ARP table,". This never happens to me. All the IP's I put in the 'static' pool, they will always be there until I manually delete them and independent
of router reboots. If your ARP clears out, that must be really annoying!!!
If a client device does not request IP
If a device does not broadcast a DHCP request, then the router does not respond. Period. If the device starts sending packets across the network using some IP address, devices on the network (including the router) will eventually associate that IP address with the MAC address that is using it and put the relationship in their ARP tables.
If a device broadcasts a DHCP request, then the router does as described above:
- If the device appears in the router ARP table (every device on the network typically maintains an ARP table, but the router knows only what is in its own ARP table), the the router says, "use this IP".
- If the device MAC address does not appear in the router ARP table, the router then looks in the Address Reservation list. If it finds the MAC address there, it responds with "use THIS IP address" (from the table).
- If the device MAC address is not in the reservation table, the router picks an IP from the dynamic pool.
If your ARP clears out, that must be really annoying!!!
Not a problem. The ARP table exists to expedite sending Layer 3 data packets (i.e. IP). Every time a process on the computer (any device on the network) wants to send an Ethernet packet, the network adapter looks at the packet to see if it is a Layer 2 packet (addressed by MAC address for the local network) or a Layer 3 packet (addressed by IP address). If it is an IP address, the network adapter has to know which MAC address to send the packet to. It first looks in the ARP table to see if the IP address is already known. If found, it now knows which MAC address to send the packet to. If not found, the computer issues an ARP lookup request, "who had IP xx.xx.xx.xx?" Some device on the network will respond, "I have this IP. Send packets for that IP to my MAC address". And the computer adds that IP address to its ARP table.
This is all automatic. Having the table eliminates the need to issue a request for every packet the computer wants to send.
One common situation people often create is having the DHCP 'pool' overlap with address reservations. For example, if the pool is 192.168.1.1 to 192.168.1.99, the user may define reservations for devices as 192.168.1.24, 192.168.1.77, 192.168.1.98 (for example). Suppose those devices are not active on the network and some other device requests an IP. The router may look and see, "oh, no one is using 192.168.1.24, so you can have that one." Then, the device connects to the network and asks for an IP, but the address it is supposed to use is already taken by another device. NOT GOOD.
So, the accepted practice is that address reservations should be in a group of IPs that are separate from the dynamic 'pool'.